Seed them INDOORS in late winter (I think 12-16 weeks before last spring frost) and grow them under shop lights for a couple months, (lights a few inches above plants, lights on 12-16 hours/day) then harden & transplant when the ground can be worked. If they get tall & leggy, trim them with scissors to about 3-4" tall.

If this sounds like too much work, you can always buy plants instead of sets.

Mark

So they're impossible to direct sow then? Do you have to space them or thin them out as they grow or will they move each other around?

Well, yes & no. See the link below from Cornell. They recommend starting 8-10 weeks before last frost...

"Can be direct-seeded, grown from transplants started inside, or from sets -- small bulbs about ½-inch in diameter grown from seed the previous season.
Choose a weed-free, well-drained location. Raised beds are ideal. Onions are good for intercropping with other garden plants, especially early-maturing spring greens. Do not plant where other onion family crops have been grown in the past 3 years.

Direct-seeding in the garden may not allow enough time for long-season varieties to mature, but is fine for shorter-season varieties or for scallions - onions harvested before the bulb forms.

Direct-seed in spring when the soil reaches 50 F. Plant seed ¼ inch deep, ½ inch apart, in rows 12 to 18 inches apart. Thin to 4-inch spacings for large bulbs, 2-inch spacings for smaller bulbs but higher yields, or 1-inch spacings for scallions.

Start transplants inside about 8 to 10 weeks before last frost date. Plant 4 or 5 seeds in each cell, or seed in flats ¼ inch deep and ½ inch apart. If tops grow too tall and begin to droop, trim back to about 3 inches tall with scissors. After hardening off, transplant 2 to 4 weeks before last frost date. Space 4 inches apart for large bulbs, 2 inches apart for smaller bulbs, or 1 inch apart for scallions..."

Here is a link that might be useful: Growing onions--Cornell

When did you start seeds that are popping up now? I read you can start seeds in August and overwinter them for harvest next year. I think the trick is not to let them grow much before winter so they don't bolt to seed next year... same with sets--you can grow small sets and replant them in the spring...

Usual time for sowing seed is very early spring. And yes you can grow good onions from seed that is sown outside.

I planted the seed around the last week of May. What defines early spring? There's snow on the ground here in NE OH until the beginning of May.

It might be a good idea to start them in flats as suggested. I'm only interested in growing scallions/table onions. Not the big bulbs.

How old were the seeds? It shouldn't take from May til now to see something. How deep did you plant the seeds and did you keep them moist?

Seed was fresh from Johnny's. Didn't plant them deep at all, but I did plant them in a lasagna bed.